In the context of setting up tables in PostgreSQL, using primary keys instead of unique constraints for ID columns is emphasized as a best practice due to several advantages in data integrity and database performance. Primary keys ensure each row in a table is uniquely identifiable and non-nullable, which maintains data integrity and prevents duplication. They also enable automatic indexing, which enhances query performance, support logical replication by serving as a reference point for data consistency, and help maintain referential integrity when used in foreign key relationships. In contrast, unique constraints, while ensuring column uniqueness, allow for null values, which can lead to ambiguous results and complicate logical replication processes since they do not serve as a default replica identity. Developers are advised to use the primary key for ID columns to avoid these complications and benefit from PostgreSQL's optimization features, with SERIAL data type recommended for auto-incrementing IDs.